Silicon, which constitutes one example of a base material of a semiconductor wafer for use in manufacturing a semiconductor device, is very hard and brittle and has a single crystal structure. For these reasons, it is very likely to be cracked in a specified direction. In addition, the integrated circuit manufacturing process has in recent years been being automatized. Under such existing circumstances, a semiconductor wafer is subjected to repeated travellings and positionings through the processes. Therefore, it is necessary to have the wafer chamfered or bevel-machined at its outer peripheral edge, to prevent its edge being broken off or chipped during the integrated circuit manufacturing process. Such damages at the wafer's edge allow small fractured pieces or powders of silicon to be produced and they, together with environmental dusts, can cause a reduction in the yield as well as a degradation in the characteristics of the integrated circuits being produced.
For the above-mentioned reasons, during the process of manufacturing a wafer, chamfering or bevelling is conventionally performed along the outer peripheral edge of a wafer. More specifically, this chamfering operation is carried out by applying a rotary working tool such as a grinding wheel against the outer peripheral edge of the wafer.
By the way, the outer peripheral region of a wafer is usually partly formed with an orientation flat (hereinafter referred to as "orientation-flat portion") for indicating the orientation of the crystalline structure across the surface, and therefore for enabling the positioning of an optical pattern or the like. This orientation-flat portion is formed by linearly grinding off a part of the outer peripheral region of the wafer.
Accordingly, chamfering of a wafer having an orientation-flat portion includes chamfering of the linear portion and chamfering of the remaining almost circular portion. As a result, the chamfering operation becomes complicated and expensive, and it is difficult to achieve a high level of chamfering precision.
In view of the above, various methods and apparatuses for effecting the chamfering of wafers have hitherto been proposed.
For instance, Japanese Patent Examined Publication No. 57-10568 discloses an apparatus in which the so-called "copy grinding" method is adopted. In this apparatus, a wafer to be chamfered is sandwiched between the seat plate of an upper shaft and the seat plate of a lower shaft and, on the other hand, a master wafer is coaxially disposed relative to the wafer to be chamfered, thereafter a grinding wheel is moved in such a manner as to follow the master wafer.
Further, Japanese Patent Unexamined Publication No. 59-224250 discloses a method of chamfering a pair of wafers simultaneously.
Although methods and apparatuses concerning the chamfering operation per se have indeed been proposed, no proposal has yet been made of a method and an apparatus therefor in which a series of steps including supply of wafers, chamfering of wafers, and transfer and recovery of wafers are performed on a full-automatic basis. The existing circumstances are that such a series of steps are carried out with the use of manpower, and that, accordingly, such an operation requires a large amount of time and labor. Enhancement in operating efficiency and reduction in labor have thus been eagerly desired.